Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatus employing a liquid-ejection recording method, an inkjet recording apparatus is known that uses a recording head (liquid-droplet ejection head) for ejecting droplets of ink. During image formation, such liquid-ejection-type image forming apparatuses eject droplets of ink or other liquid from the recording head onto a recording medium to form a desired image. Such liquid-ejection-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving the carriage with the recording head in a main scanning direction, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus as the recording medium is conveyed thereto.
Such a liquid-ejection-type image forming apparatus may have multiple recording heads to eject liquid droplets of different colors to form a composite color image or a line-type recording head unit in which multiple recording heads are arrayed in a direction in which nozzles are arrayed in each of the recording heads. In such configurations, the multiple recording heads are relatively positioned at high precision to increase the accuracy of positions at which droplets ejected from each of the multiple recording heads land on a recording medium to form a high-quality image.
In addition, if ejection failure occurs in one or more of the multiple recording heads, it is necessary to replace a defective recording head with a new one while reproducing the highly-precise positioning of the heads.
Hence, conventionally, for example, JP-20030154724-A proposes a head holder that collectively holds the multiple recording heads and is mounted on a carriage so that the position of the head holder is adjustable. In addition, JP-2010-30271-A proposes to hold a nozzle plate or channel plate formed at high precision with respect to X, Y, and Z directions in contact with ribs of a base member.
JP-H07-314851-B proposes a head position adjustment mechanism that includes recording heads, a carriage, and urging springs. The carriage has head positioning faces to position the recording heads in a sheet feed direction parallel to a scanning shaft of the carriage and head guide grooves perpendicular to the scanning shaft. The recording heads have engagement portions to engage the head guide grooves to restrict movement in the scanning direction and contact faces formed back and forth in the scanning direction corresponding to the head positioning faces. The urging springs urge the contact faces of the recording heads against the head positioning faces of the carriage. With reference to on one head brought into contact with one head positioning face, the other heads are brought into contact with the other head positioning faces via a required number of adjustment plates to adjust relative positions between the recording heads.
JP-2002-316415-A proposes to accurately finish by a machining finish device a reference face of each head abutment section of a frame body to which multiple head chips are inserted, in order to determine relative positions of the multiple head chips in adjustable manner by shifting respective heads with each other at certain intervals in a direction in which nozzles are arrayed in row.
However, for the configuration described in JP-20030154724-A, head replacement need be performed in unit of the head holder including the multiple recording heads. For the configuration described in JP-2010-30271-A, a portion of the nozzle plate or channel plate that contacts the ribs need be formed at high precision.
The configuration described in JP-H7-314851-B requires a complex position adjustment mechanism, thus increasing cost of the carriage. In addition, such a complex position adjustment mechanism tends to be difficult to apply to the multiple recording heads. The positions of all recording heads need be readjusted in replacing a reference head of the multiple recording heads, thus hampering easy head replacement.